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    Re: Question about PSM and understeer

    Silver Bullet said:There is no opinion here or on any Porsche Forum that I value more than Carlos', but I have to disagree with this one.

    What Carlos seems to be saying is that in an oversteer situation (real wheels slipping), PSM will correct by inducing understeer (front wheels slipping). All 4 wheels would then be slipping. That is, PSM would induce a 4 wheel drift, which is the most dangerous situation in driving.

    In my experience, PSM is very good at dealing with oversteer and the correction, while it can be abrupt and unpleasant (especially to have control snatched away from you when you may be comfortable with the slide), has not lead me to feel any understeer.

    Thank you for your kind words. I think we agree in part, that reaction you mention with oversteer and PSM correcting it by cutting the impulse of the car is I what I mention that happens to me too when oversteer is not excesive and induced progresively (like when progresively applying throttle exiting a curve). But when its brought about suddently and violently and its too much too quick, the effect of PSM is different, stopping the car would not do, and the result is that you get understeer and run wide. For example in a tight curve (the steering angle is great) with ice, you suddently floor the gas on purpose (a comon PSM excercise) to make it spin, the car won't spin, but it turns out that it goes wide, and you lock the steering further and again there is not spin, there is understeer. PSM is not inducing a 4 wheel drift since PSM acts on all four wheels independantly and in case of oversteer were the rear wheels loose traction, PSM slows the inside rear wheel and the outside front wheel, that has the effect of ranging from neutralising the oversteer to inducing understeer. So all in all if you are constantly having the PSM intervene (not a good sign) you wil find that the car understeers more times than with PSM off.

    Silver Bullet said:
    Another word about over and understeer and PSM: unless you are a very very good driver, your lap times will almost certainly be better with PSM on than off. That is because both over and understeer slow you down, and PSM helps to manage them. If you are brave enough to push yourself with a timer, give it a try: most people will find exactly what I just wrote. Only the best (most experienced drivers) are faster with PSM off. Warning though: pushing yourself on a dry track with PSM of can be a dangerous thing to do. A slicked skid pad is the best place to demonstrate this because it can all happen at much slower speeds. There is a nice exercise at the Porsche Sport Driving School that illustrates this.

    I agree 100%. The only reason I turn OFF PSM is to be able to learn more from the reactions and mistakes at the limit without the PSM taking over and depriving me of the experience, its a quicker learning curve that way. But ideally it should have to come on except for certain curves and special situations were it gets in the way of the correct line. I didn't spin any of the cars on Wednesday, not even the Turbo, but was close several times because I was testing the limit and I'm far from a pro. Still in a very fast track I would be hesitant to turn off PSM because with high speeds a mistake can be irrecuperable and very dangerous. And now even less because with the sportchrono sport setting of the PSM in the 997's its great because you really have to loose it for it to act. Personally I wouldn't buy a car that I'm going to be driving spiritedly on the street without PSM.

    Re: Question about PSM and understeer

    ResB said:
    I will give it a go next time I'm on the track. I'm hoping that with PSM off, my times/experience of the track will be quicker/more involved. Having said this though, currently with PSM on, the car has not stepped out of line insofar as oversteer is concerned, perhaps because PSM allows the car to understeer more, so I wonder if I have more room in the corner before I feel the back end starting to go, therefore giving rise to better lap times. (Or at least keeping up with my mate )

    On reflection I have to say, with PASM/Sport mode engaged I still had quite a bit of understeer, but the car did feel better particularly on exit from any bend.

    I need to explore this topic a little more at the track and I'll log it with the performance box if I can get away with it. Should be interesting getting the results I'm sure.

    I wouldn't have too much hesitation in turning PSM off at the track if it is a grass track (no walls) and if you are prepared to take it easy and gradually increase the speeds. Otherwise, I'd be reluctant.

    I suspect that you feel understeer because that is the nature of a rear wheel drive beast. I don't think that turning PSM off will get rid of the understeer you feel.

    I feel it at the track too, and it is irritating, but the way to deal with it is to be smooth, and to respect it: the car is telling you that you are asking too much of the front wheels.

    Re: Question about PSM and understeer

    Carlos from Spain said:Personally I wouldn't buy a car that I'm going to be driving spiritedly on the street without PSM.

    I completely agree. The facelifted 997S looks like a very attractive car for me now given that it will have 385 hp, PSM, -20 mm suspension option in NA (hope hope) and LSD (not to mention iPod compatibility)!

    GT3 in 5-10 years!



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